Instruction manual

Force Imaging

Force Calibration (TappingMode)

Rev. B MultiMode SPM Instruction Manual 199

11.5 Force Calibration (TappingMode)

Force Mode allows the imaging of forces between the tip and surface, including chemical bonds,

electrostatic forces, surface tension and magnetic forces. In TappingMode, you can observe forces

by measuring changes in tip RMS amplitude, phase, or TM deﬂection. The user may collect force

plots in one of two forms: Force Plot and Force Volume. The two forms are similar, with Force

Volume generating a map of many individual force plots. To produce high-quality force plots, it is

necessary to precisely control tip position relative to the surface.

11.5.1 Force Plots

When performing Force Plot in TappingMode, the piezo moves to the center of the current X-Y

scan, then turns off the X-Y scan motion. Next, a triangular waveform is applied to the Z electrodes

of the piezo tube resulting in the sample moving up and down relative to the oscillating tip. The

same Z-axis piezo motion occurs in Contact Mode AFM force plots. However, in TappingMode, the

force plot is a graph of the piezo’s extension versus oscillating tip amplitude, phase or TM

deﬂection, instead of deﬂection or friction.

Uses of Force Calibration in TappingMode include characterizing forces on the cantilever tip,

diagnosing SPM performance, calibrating the RMS amplitude or TM deﬂection, and conﬁguring

Lift Mode. For example, as the oscillating tip is brought closer to the surface, tip motion is

dampened, which shows as an immediate drop in amplitude. When plotted, the graph resembles

Figure 11.5a.

CAUTION: Because TappingMode cantilevers are relatively stiff, Force Mode

can potentially damage the tip and/or surface. Before using Force

Calibration, read and understand the following section.